Band tesnion arrangements for drafting machines



May 29, 1956 M. SANDERS 2,747,283

BAND TENSION ARRANGEMENTS FOR DRAFTING MACHINES Filed June 18, 1954 =r v V I A F \J T I i INVENTOR.

Fig. 3. Morris Sanders JH for my BAND TENSION ARRANGEMENTS FOR DRAFTIN G MACHINES Morris Sanders, Rochelle Park, N. J.

Application June 18, 1954, Serial N0. 437,708

1 Claim. (CI. 33-79) My invention relates to a drafting machine comprising a fixed member clamped to a drawing board, an arm pivoted at one end of the fixed member, a second arm pivoted at one end to the moving end of the first arm, and a drafting head carried at the free end of the second arm and movable over the drawing board. The drafting head includes a protractor and a protractor arm provided with a Vernier or witness point and with means for holding one or more rulers or straight edges which can be rotated about the protractor. As the drafting head is moved over the drawing board, orientation of the protractor is held constant by a combination of pulleys and bands.

Heretofore the arrangement of drafting or parallel motion machines of the endless band and pulley type has been such that the only means for maintaining the complete assembly of all sections of the machine have been the bands which are tensioned about the pulleys. As these instruments are used under all climatic and temperature conditions, band breakage occurs frequently. In the event such breakage should occur on an inclined or vertical board, or on shipboard where these instruments are used for navigational purposes, the section within which the breakage occurs could become disassembled and fall to the floor, thus causing damage to the instrument. Normally band replacements are a relatively simple matter and spare bands can be carried and replaced readily in the event of breakage. However, in the event of damage due to the dropping of the machine to the floor when used on board a ship, the instrument could become useless.

Therefore, one object of my invention is to provide a parallel motion machine of the band and pulley rotatable section type wherein these sections will retain their assembly regardless of band breakage.

A further object of this invention is to provide a parallel motion drafting machine of the band and pulley type wherein one section is free to rotate within or about the other and at the same time prevents the rotating of the tubes while the bands are being tensioned, and to accomplish this without resorting to auxiliary means such as auxiliary pins etc.

Another object of this invention is to provide a drafting or parallel motion machine having the major portions of its arms made of light-weight material such as aluminum, and at the same time to provide means at the band tensioning section to have a material of great wear resistance such as steel, to withstand the pressure applied to it during the tensioning of the bands.

Still another object of my invention is to provide means to instantly free the pulley from band tension, and instantly return it to its original band tension without resorting to the loosening or tightening of band tensioning nuts.

With the foregoing and other objects in view which will appear as the description proceeds, the invention consists of certain novel details of construction and combinations of parts hereinafter more fully described and pointed out States Patent 2,747,283 Patented May 29, 1956 2 in the claim, it being understood that changes may be made in the construction and arrangements of parts without departing from the spirit of the invention as claimed.

In the accompanying drawing a preferred form of the invention has been shown.

In said drawing:

Figure 1 is a reduced plan view of the entire drafting machine in parking position;

Fig. 2 is a fractional sectional view of the upper arm or anchor to elbow section of the machine of Fig. 1;

Fig. 3 is a sectional view of the lower arm or elbow to protractor section of the machine of Fig. 1;

Fig. 4 is an enlarged detailed top plan view of a pin; and,

Fig. 5 is an enlarged detailed side view of the pin of Fig. 4.

Similar reference characters refer to similar parts throughout the several views.

In the drawing the numeral 1 denotes an anchor plate mounted on a drawing board (not shown). Swiveling on the anchor plate 1 is a hinge mounting to which the anchor bracket 3, within which is an anchor pulley 4, is fastened and around which the anchor bracket 3 rotates. The upper arm of the drafting machine consists of the anchor bracket 3 and an elbow bracket 5, which are held in alignment by the upper tube 6. Within the anchor bracket 3 and the elbow bracket 5 are the anchor pulley 4 and an elbow pulley (not shown), on which an endless band 8 runs. This band 8 is tensioned by the tensioning nut 9. Band covers preferably are provided to guard the band 8. The lower arm has a lower elbow bracket 10 and a head bracket 11. Within the elbow bracket 10 and the head bracket 11 are the elbow pulley and a head pulley on which an endless band 12 runs. A lower tube 13 provides alignment, and a tensioning nut 14 is used to tension the band 12. The head bracket 11 has attached to it, and rotates around, a head section. Said head section consists of a protractor 15 (Fig. 1) which can rotate around a witness plate 16. A base plate 17, which holds a rule or scale 18 moves with the protractor to any angular setting and can be locked in place by a scale lock 19. A thumb piece 20, which has a pinion attached toit can be used to operate a gear (not shown) within the head, in order to move the protractor for fine angular settings. A protractor lock 21, when released, allows for any base line setting of the scale 18. A knob 22 provides for easy movement of the head about the drawing board or table. Thumb screws located on the elbow brackets 5 and 10 operate brakes of the brake disk type against the bands 8 and 12 at a point where they contact the elbow pulley 7, thus preventing slippage of the machine when used on inclined boards.

The band tensioning arrangement of the upper arm comprises the upper tube 6 one end of which is free to rotate about a tube support 24 (Fig. 2) which is held to the anchor bracket 3 by a screw 25. At the other end of the upper tube 6 is press fitted a coupling plug 28 a portion of which is also press fitted into a tube coupling 29 which is threaded on one end and has a slot 40 on the other end to receive the shaft portion of a screw 31, which is secured into, and extends through, the Wall of the elbow bracket 5. Before pressing the coupling plug 28 into the coupling tube 29 the nut 9 is threaded into the tube coupling 29. The end of the nut 9 is brought against the end of the elbow bracket 5 with the washer 30 between them. To tension the band 8 it is only necessary to turn the nut 9 until the desired band tension is obtained. Turning of the upper tube 6 and the tube coupling 29 is prevented by the shaft portion of the screw 31 in the slot of the tube coupling 29 while tensioning the band 8, but the elbow section of the upper arm is free to rotate about the tube support 24 to give the machine flexibility. The thrust of the upper tube 6 against the anchor bracket 3 is taken by a thrust washer n the e e t of a hand re a e d ss h y of the p er a m s pre en a n e b e c w i fi e int t e lo ed s o Of t u c up ing n t the other end by the shaft portion of the screw 2;7 fitted into an annular groove 41 of the tube support 24.

The and h n ns r n m nt o he lower arm comprises the lower tube 13, which has press-fitted into it at one end a thrust plug 34 and is free to rotate in the head bracket 11. The other end of the tube 13 is simila ly cons r c ed to h o e upp r t The thrust of the tube during tensioning is taken by the thrust P ug 34 ains an nd P u 3 iden el d m y is prevented on one end by the shaft portion of a screw 32 titted into a groove 36 of the thrust plug 34, and on the other end by the same arrangement as that shown in Fig. 2. Desired tension is obtained by turning the nut 14.

The thrust plug 34 has, in addition to the aforementioned annular groove 35, a second annular groove 35, and its one end portion 37 is ball-shaped, while its other end portion 38 is tapered and formed as a socket for a ball 42.

The shaft portion of a screw 43 extends into the annular groove 35, which is of such a width as to allow a limited axial movement of the plug 34 relative to the tube 13. A pin 44 is rotatably mounted in the tube 13 and has a flattened end portion 45 as well as a recessed center portion 47 adjacent the ball 42. The pin .4 is intended to act as a cam member, and a lever 50 is secured to the end portion 45 of the pin 44 by means of a screw 51 or the like, and has as its free outer end portion a protrusion 53, which is adapted to snap into a notch 5.4 in the tube 13. If the parts 44 and 50 are in the position shown in Fig. 3, the rounded section of the portion 47 of the pin 44 forces the bolt 34 against the end plug 33, so that the band 12 is tensioned. If the lever 50 is moved about ninety degrees relative to its position of Fig. 3, the recessed center portion 47 faces the ball 42 and the pulley is freed from tension of the band 12 instantaneously.

Since certain changes may be made in the above article and different embodiments of the invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claim is intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which as a matter of language might be said to fall therebetween.

Having thus fully described my said invention, what I claim as new and desire to secure by Letters Patent is:

In a drafting machine of the band and pulley type, which has pivoted to each other a pair of arms each of which is provided at each end with a bracket that has a tubular portion and contains a pulley on which runs an endless band, a band tensioning arrangement comprising a tube having one of its end portions slidably extended into the tubular portion of a first one of said brackets,

a longitudinal member being slidably extended into the aforementioned end portion of said tube and having annular grooves in both of its end sections, a first screw extending through the tubular portion of said first bracket into the first one of said grooves in said longitudinal member, a second screw extending through said tube into the second one of said grooves in said longitudinal memher, a cam member adjacent one end of said longitudinal member being rotatably extended through said tube, a thrust receiving member adjacent the other end of said longitudinal member being provided on said first bracket, an operating lever secured to said cam member outside of said tube for turning said cam member, a sleeve mem her extended from and secured to the other end portion of said tube being partially extended into the tubular portion of a second one of said brackets, means for preventing a rotation of said tube relative to said second bracket being provided on said sleeve member, and a nut screwed upon that portion of said sleeve member which is not extended into said second bracket and extends beyond the tubular portion thereof.

References Cited in the file of this patent UNITED STATES PATENTS 2,178,046 Little Oct. 31, 1939 2,481,666 Hislop Sept. 13, 1949 FOREIGN PATENTS 602,231 Great Britain May 21, 1948 

